Rotating equipment can be utilized in many manufacturing applications. Rotating equipment failures can cause lost production time, injury to personnel, and/or loss of capital equipment. One possible cause of rotating equipment failure can be failures due to excessive vibrations. Accordingly, some rotating equipment can be operated with at least one proximity probe, such as an eddy current proximity probe that can be adapted to continually monitor vibrations (e.g., radial displacements of a rotating part) to detect vibration values in excess of a predetermined threshold.
Proximity probes or proximity measuring systems can be used for the measurement, monitoring, and/or analysis of axial and/or radial shaft vibration (peak-to-peak displacement amplitude) in rotating machinery. A proximity probe or transducer can be placed in a position defined by a mount. Read-outs from proximity probes, such as via oscilloscope, meter, and/or x-y recorder, might not provide an accurate indication of the shaft motion relative to the proximity probe or transducer.
Instead, data provided by the probe can reflect movement of the shaft relative to the probe, electrical properties of the shaft, and/or inaccuracies generated by the probe itself. The impact of shaft movement can be referred to as “mechanical runout”. The impact of the electrical properties of the shaft can be referred to as “electrical runout”. The impact of the probe's inaccuracies can be referred to as “probe noise”.
Eddy current proximity probes can derive distances, such as proximities, utilizing induced electrical currents in the material of the rotating part. Some level of inaccuracy in the values obtained from the probe can be present, however, which can be due to any number of factors, such as instrumentation error, mechanical runout, and/or electrical runout, etc., any of which can vary with measurement location. Electrical runout, often called glitch, can result from variations in electrical properties of the shaft material.
Causes for mechanical runout can comprise aberrations in cross-sectional shape and/or axial flatness, etc., bearing hydrostatic effects, bearing hydrodynamic effects, etc.
A possible test procedure, to assess inaccuracies comprised in values obtained from the probe, can involve rotating a shaft at a speed below and/or far below a normal operating speed. Such a test procedure can be referred to as a “slow roll” test. A displacement signal that a proximity probe provides during a slow roll test can be called a “slow roll value”.
Shaft vibrations can be measured by a probe, which can be an inductive sensor. Probes can be configured to measure vibrations caused by a rotation of a shaft. When the shaft is rotating at a relatively slow speed (e.g., less than 250 RPM) a slow roll vibration (“slow roll”) can be measured. A portion of slow roll can be due to mechanical defects of the shaft surface and/or defects in the shaft material properties. Slow roll can affect shaft vibration readings. Slow roll can cause a manufactured shaft not to achieve one or more pre-defined manufacturing specifications.
A portion of slow roll can be caused by defects in material properties that can create uneven magnetic properties of the shaft that is read by the probe. Defects can include residual stresses in the shaft material, uneven grain size of the material, mechanical runout of the shaft, and/or shaft magnetism caused by certain non-destructive test methods, etc. In certain exemplary embodiments, proximity transducers can operate in the presence of magnetic field, as long as the field is uniform or symmetrical and not localized to a particular location on the rotor. If different levels of magnetism exist on the shaft surface such that one portion of the surface is highly magnetic while another portion is at a lower magnetic level and/or nonmagnetic, an electrical runout condition can arise. The electrical runout condition can be due to a change in sensitivity on the shaft surface to an applied field from the probe.
Rotating equipment can have a maximum specified slow roll value above which the rotating equipment is considered inoperable since the slow roll can mask shaft movement due to dynamically variable vibration. Hence a system and method to reduce electrical runout in shafts to reduce slow roll is disclosed.